1. Sort lentils and discard any debris. Rinse and drain lentils.
2. In a 2- to 3-quart pan, bring about 1 quart water to a boil over high heat. Add lentils, stir to separate, and simmer, uncovered, just until they are tender to bite but not soft, 5 to 10 minutes for Red Chiefs, 20 to 30 minutes for regular lentils. Drain.
3. Mix vinegar, oil, and garlic. Pour over warm lentils and gently mix. Let stand until cool.
4. Add bell peppers, onions, tomatoes, cucumber, basil, and feta cheese. Mix gently with lentils. Pour into a serving bowl. Add salt and pepper to taste.