Core, seed, and rinse peppers. Cut each pepper into fourths. In a large re-sealable plastic bag, place sweet pepper chunks.
In a small bowl, combine garlic, salt, olive oil, balsamic vinegar, and pepper; mix well; pour over pepper chunks. Reseal bag and shake to distribute sauce.
Preheat Barbecue grill.
Remove peppers from sauce. Place peppers, smooth-side down, on hot grill. Cook 6 to 8 minutes (turning occasionally) or until lightly charred on both sides.
Remove peppers from grill; either leave in chunks or slice into 1/2-inch-wide strips.
Arrange chunks or strips on a platter, alternating colors. Sprinkle with crumbled feta cheese.