Cook pasta according to package directions, omitting salt and fat. Drain well.
Heat the oil in a Dutch oven over medium-high heat. Add onion and pepper; sauté 5 minutes. Add garlic to pan; sauté 2 minutes or until onion is tender. Stir in tomatoes; bring to a boil. Reduce heat, and simmer 5 minutes, stirring occasionally. Add spinach to pan; cook 30 seconds or until spinach wilts, stirring frequently. Remove from heat. Add pasta and 3/4 cup cheese to tomato mixture, tossing well to combine. Spoon pasta mixture into an 11 x 7-inch baking dish lightly coated with cooking spray; sprinkle evenly with remaining 1/2 cup cheese. Bake at 375° for 15 minutes or until cheese melts and begins to brown.