Preheat the oven to 375°F. Lightly coat a 9-by-13-inch baking dish with nonstick cooking spray.
Spread the frozen meatballs in the prepared baking dish. Bake for a few minutes, just until they begin to thaw and soften enough to stir.
While the meatballs are in the oven, chop the green bell pepper and red onion.
Remove the baking dish from the oven. Pour both jars of pizza sauce over the meatballs. Add crushed red pepper flakes and Italian seasoning to taste, then stir until the meatballs are coated.
Dollop the ricotta cheese over the sauced meatballs.
Scatter the black olives, chopped bell pepper, and chopped red onion evenly over the casserole.
Sprinkle about half of the shredded Italian-blend cheese over the vegetables.
Pull the crescent-roll dough apart into pieces and scatter the pieces over the casserole.
Arrange pepperoni over the dough, then top with the remaining shredded cheese. Finish with a little more Italian seasoning and crushed red pepper, if desired.
Bake uncovered for about 30 minutes.
Loosely lay a sheet of aluminum foil over the top without pressing it into the cheese. Bake for about 10 minutes more, until the crescent dough is cooked through, the center is hot, and the casserole reaches 165°F.
Let the casserole rest for a few minutes before scooping and serving.