1. In a large pot, sauté onion in oil until golden; remove to mixing bowl.
2. Fill pot with water and cook pasta according to package directions. While pasta is cooking, add basil, garlic, salt, and pepper to the sautéed onions, and stir to combine.
3. Drain pasta and return to pot. Over low heat, add the cheese to the pot and stir until melted. Add onion-seasoning mixture and mix until well combined. Stir in tomato halves until heated through. Remove from heat and garnish with sunflower seeds.