Cook pasta according to package directions; drain. Keep warm.
Meanwhile trim fat from beef. Cut steak or tri tip into strips about 1 inch wide, 2 inches long and 1/8 inch thick. In wok or large nonstick skillet, heat 1 to 2 tablespoons oil over medium-high heat until hot. Split beef and garlic into two batches and stir-fry one at a time, cooking until outside surface is no longer pink, about 2 minutes. Remove from pan with slotted spoon; season with salt and pepper. Keep warm.
In same pan, heat 1 tablespoon oil until hot. Add mushrooms and bell pepper strips; stir-fry until mushrooms are tender. Return beef to pan; add sliced basil and toss.
Place pasta on large deep oval platter; arrange beef mixture on pasta. Sprinkle cheese over beef and pasta or pass separately, if desired. Garnish with basil sprigs and bell pepper rings.
