This recipe is recipe from an old friend of mine who ran a catering business in Oxford. He looked like a red-headed Rick Astley; only person I ever knew who used a cigarette holder, and of course he smoked Salem 100s menthol.
Sauté in olive oil 1 pound of mushrooms, sliced or cut in quarters, with 1 large red pepper, cut into strips, one a large red onion, sliced, and 3 cloves garlic, minced. Cool, add balsamic vinegar, thyme, and fresh ground pepper. Salt to taste. Refrigerate before serving.