Cook pasta according to package directions, omitting salt and fat. Drain, reserving 1/2 cup pasta water.
Heat oil in a large nonstick skillet over medium-high heat. Add onion; sauté 2 minutes. Add bacon bits; sauté 2 minutes. Add tomato, garlic, and oregano; sauté 30 seconds. Remove from heat.
Add pasta, reserved pasta water, salt, and pepper. Stir well, and cook 1 minute or until thoroughly heated and liquid is absorbed. Remove from heat; cover and let stand 3 minutes. Sprinkle with cheese.