For the panzanella: Heat a grill or grill pan. Toss the zucchini, tomatoes, and onions gently with olive oil and salt and grill until cooked through. Flip halfway through cooking.
Toss the bread cubes with vinegar, garlic, 1 tablespoon olive oil, a sprinkle of water, and salt.
Chop the grilled vegetables and add to the bread mixture. Toss gently together and season with salt, to taste.
For the blossoms: Heat the oil to 375 degrees F.
Whisk together the cake flour, baking powder, pinch salt, and club soda.
Spoon the goat cheese into a piping bag and cut a hole in the bag. Gently fill each zucchini blossom with goat cheese.
Dip each blossom into the batter and then carefully place into the hot oil. Cook until lightly puffed and golden. Remove the blossoms from the oil and drain on a paper towel. Season with salt immediately.
Fry the basil leaves until just crisped. Set aside.
For the salad: Toss the arugula with the oil, salt, and a splash of vinegar. Divide the arugula among 4 plates. Mold the panzanella into a ring mold and place on a plate. Repeat with remaining plates. Top each panzanella portion with 1 fried blossom. Drizzle with olive oil to finish and top each plate with a fried basil leaf.