While you're making these, grill other vegetables, such as portobello mushrooms, zucchini, and fennel, as well. Brush with oil and season with salt and pepper before grilling. Serve them all on a platter with the vinaigrette drizzled over the top.
Brush grill with oil; heat to medium hot. Grill peppers until blackened, 8 to 12 minutes. Let peppers cool in a paper bag. Peel and seed, saving juices. Cut into 1-inch strips.
In a bowl, combine garlic, vinegar, thyme, salt, pepper, and any pepper juices. Gradually whisk in oil. Toss peppers with vinaigrette, and arrange on a platter to serve.