Preheat oven to 425°F. Roast cauliflower, peppers, and onion on separate pans with oil and salt until tender and caramelized, about 30-35 minutes.
Cook pasta until al dente, drain, and return to pot. Mix in 2 cups marinara, basil, and ½ cup mozzarella.
Layer 1 cup marinara in a 9x13-inch dish, add half of pasta mixture, roasted vegetables, dollops of cottage cheese, and ½ cup mozzarella. Repeat with remaining ingredients.
Place a baking sheet underneath and bake uncovered at 425°F for 30 minutes, then broil for 2-5 minutes until cheese is golden. Cool for 10 minutes, garnish with basil, and serve.
Notes
Use fresh basil for the best flavor and keep an eye on the cheese during broiling to prevent burning.