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 set 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 reduced 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 teriyaki: Whisk together the tamari, 2 tablespoons water, the vinegar, agave, garlic, ginger and sesame oil. Pour half of the sauce in a small saucepan and cook over medium heat until reduced by half, 6 to 8 minutes. Reserve for a later use.
Meanwhile, heat a large saute pan over medium heat and add the other half of the teriyaki sauce and the Spam. Cook on each side for 2 to 3 minutes. Remove the Spam and reserve to build the musubis, and discard the sauce.
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 (a 3-by 4-inch rectangle). Place 1/4 cup of the pineapple rice over the mayo and top with 1 piece of the Spam. Place 1/4 cup of the rice on the Spam and dollop 2 teaspoons of the mayo over the rice. Fold the nori sheet over filling, then tuck in the sides and roll up into a tight bundle, as you would a burrito. Wrap the musubi tightly in the plastic wrap. Repeat this process with the remaining ingredients to form 8 musubis. There will be some leftover rice. 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 teriyaki 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.