To make the marinara sauce, in a heavy skillet, heat 1 tablespoon of the olive oil over medium-high heat. Add tomatoes, salt, garlic, chopped onions, basil, sugar, oregano and black pepper. Simmer uncovered until the sauce thickens, about 30 minutes.
Prepare a hot fire in a charcoal grill or heat a gas grill or broiler. Away from the heat source, lightly coat the grill rack or broiler pan with cooking spray. Position the cooking rack 4 to 6 inches from the heat source.
Brush the red peppers, squash, zucchini and sweet onion with the remaining tablespoon of olive oil. Place the vegetables on the grill rack or broiler pan. Grill or broil, turning as needed, until the vegetables are tender, about 5 to 8 minutes. Transfer the vegetables to a bowl and set aside.
Fill a large pot 3/4 full with water and bring to a boil. Add the pasta and cook until tender (al dente), about 10 to 12 minutes, or according to package directions. Drain the pasta thoroughly.
Divide the pasta evenly among individual plates. Top with the marinara sauce and grilled vegetables. Serve immediately.