Preheat oven to 400°F (200°C).
Prepare ingredients: Drain and rinse the lentils. Chop all vegetables into ½-inch (1.25 cm) pieces.
Assemble the sheet pan: On a large baking sheet, add the gnocchi and lentils. Top with cherry tomatoes, chopped bell peppers, zucchini, and red onion.
Season: Drizzle with olive oil and sprinkle with Italian seasoning, salt, and pepper. Toss everything to coat evenly.
Bake: Roast in the oven for 25 minutes, tossing everything halfway through at the 15-minute mark for even cooking.
Garnish & Serve: Once baked, top with fresh parsley and drizzle with chili oil if desired. Serve warm and enjoy!