For the homemade "Spam": Set a rack in the middle of the oven and one on the bottom. Preheat the oven to 375 degrees F.
Pulse the ice cubes in the bowl of a food processor until very fine (similar to the texture of crushed ice). Add the chicken, pork, 1 1/2 teaspoons salt, 1/2 teaspoon pepper, the garlic powder, onion powder and sugar, and pulse until blended.
Spray a quarter baking sheet with cooking spray and use your hands to evenly press the meat mixture into the baking sheet, pushing all the way to the edges. Fill a large baking dish halfway with hot water and place on the bottom rack of the oven. This will create steam in the oven and keep the meat moist. Place the meat on the middle rack and bake until just cooked through and firm to the touch, 15 to 20 minutes. Set aside to cool completely.
Whisk together the hoisin sauce, soy sauce and vinegar. Carefully flip the meat onto a large cutting board and cut in to 8 equal pieces, about 2-by-3 1/2-inches each. Spray a large cast-iron pan or griddle with cooking spray and heat over medium-high heat. Working in batches, cook to brown the meat, about 2 minutes per side, brushing with the hoisin glaze during the last few seconds of cooking. Reserve any remaining glaze.
For the rice: Add the stock and rice to a medium saucepot set over medium heat. Bring to a low simmer then cook, covered, until the rice is tender and the liquid is absorbed, about 15 minutes.
Meanwhile, pulse the cauliflower in a food processor until it resembles a rice consistency, about 4 cups total. Bring 1 1/2 cups water to simmer in a large saute pan set over medium heat. Add the cauliflower and cook, covered, until just tender, about 3 minutes. Drain the cauliflower, then pat dry with paper towels. You should be left with about 2 cups of cooked cauliflower.
Wipe out the large saute pan, then add the olive oil and place over medium heat. Add the bell peppers, pineapples and jalapenos, and cook until tender and slightly browned, about 5 minutes. In a large bowl, mix together the cilantro, vegetables, rice, cauliflower and some salt, and stir to combine.
For the mayo: Pour the pineapple juice in a small saucepan and bring to a simmer over medium heat. Cook until the juice reduces to 2 tablespoons, 8 to 10 minutes. Set aside to cool.
Whisk together 1 tablespoon plus 1 teaspoon of the pineapple reduction, the yogurt, mayonnaise, lime juice, Sriracha and 1/4 teaspoon salt in a mixing bowl. Taste the sauce and if it needs a touch more sweetness, add the remaining 2 teaspoons pineapple reduction.
For the musubis: Place a large piece of plastic wrap on a clean work surface. Place one nori sheet, rough-side up, in the middle of the plastic wrap. Spread 2 teaspoons of the mayo in the center of the nori (about 3-by-4-inches). Add 1/4 cup of the rice mixture on top of the mayo and top with a piece of the homemade "Spam." Place 1/4 cup of the rice mixture on the top and dollop 2 teaspoons of the mayo over the rice. Fold the nori sheet over the filling, then tuck in the sides and roll into a tight bundle, as you would a burrito. The formed musubi should be around 4-by-2 1/4-inches. Wrap tightly in the plastic wrap. Repeat this process with the remaining ingredients to form 8 musubis. There will be some leftover rice after all of the musubis are formed. Rest the musubis in plastic wrap for at least 5 minutes.
Whisk together the flour, 1/2 teaspoon salt and 1/4 teaspoon pepper in a shallow baking dish. Whisk the egg whites with 1/8 teaspoon salt in a second shallow baking dish. Stir together the panko breadcrumbs, plain breadcrumbs, 1 teaspoon salt and 1/4 teaspoon pepper in a third shallow baking dish. Unwrap and coat two musubis in the flour, and tap off any excess. Coat the musubis in the eggs and allow any excess to drip off. Then coat the musubis in the breadcrumbs.
Add 1 tablespoon of the olive oil to a medium skillet set over medium heat. Add the coated musubis and cook until crisp on each side, about 5 minutes total. Transfer to paper towels to drain any excess oil. Repeat the breading and pan-frying process for the remaining musubis, adding 1 tablespoon of the olive oil to the pan before each batch.
Drizzle the musubis with some spicy mayo and hoisin glaze (about 1 tablespoon of mayo and 1 teaspoon of glaze per musubi) and serve immediately.
If making the musubis ahead of time, reheat in a 350 degree F oven until warmed through, 10 minutes.