Cook pasta to desired doneness as directed on package.
Meanwhile, in small nonstick saucepan, cook onion and garlic in oil until tender. Stir in tomatoes, oregano and cumin. Bring to a boil over medium-high heat. Boil 4 minutes or until slightly thickened, stirring frequently to prevent sticking. Remove from heat.
Drain pasta; rinse with cold water. Drain well. In large bowl, combine cooked pasta, roast beef, corn, chopped tomato, bell pepper and cilantro; mix gently.
Add tomato mixture; toss gently until well mixed. Serve immediately, or cover and refrigerate until serving time. If desired, serve on lettuce-lined plates and garnish with tortilla chips and additional cilantro.