In a 5- to 6-quart pan over high heat, bring 3 quarts water to a boil. Add orzo and cook just until tender to bite, about 10 minutes. Drain orzo and return to pan.
Meanwhile, rinse peppers; stem, seed, and finely chop.
In a food processor, purée butter, basil, and garlic.
Add butter mixture to orzo. Stir over medium heat until butter is melted and pasta is hot.
Stir in peppers, tomatoes, cheese, and capers. Pour onto a rimmed platter and serve hot, warm, or at room temperature.