Preheat the oven to 350°F (175°C).
Heat a large skillet over medium heat. Add the chorizo and cook, breaking it up, until no longer pink, about 5–7 minutes; drain excess fat.
Stir the marinara sauce and canned diced tomatoes into the cooked chorizo, bring to a simmer, and cook for about 3 minutes to reduce excess liquid.
Cook or prepare the tortellini according to package directions if not pre-cooked, then drain well.
Spoon a thin layer of the sauce into the bottom of a 9x13-inch (or similar) casserole dish.
Toss the tortellini with the remaining sauce in the skillet until evenly coated. Add half of the sauced tortellini to the casserole dish.
Layer half of the pepperoni, sliced olives, sliced green bell pepper, sliced red onion, and half of the mozzarella over the tortellini.
Add the remaining sauced tortellini, then top with the remaining pepperoni, olives, peppers, onion, and mozzarella.
Bake in the preheated oven for 25 minutes, then, if desired, broil on high for up to 5 minutes to brown the cheese—watch closely to prevent burning.
Remove from the oven and let rest briefly, then serve.
