1. Coat a large nonstick skillet with cooking spray; add oil. Place over medium-high heat until hot. Add pepper strips, zucchini, and onion; cook 5 minutes, stirring often. Add 1/2 cup broth and thyme. Cover, reduce heat, and simmer 5 minutes.
2. Combine remaining 1/2 cup broth and flour, stirring well. Add to vegetable mixture, stirring well. Cook, stirring constantly, until slightly thickened and bubbly.
3. Prepare grill.
4. Rub steaks with garlic halves, and sprinkle with 1/2 teaspoon black pepper. Coat grill rack with cooking spray; place on grill over medium-hot coals (350° to 400°). Place steak on rack, and grill, covered, 4 minutes on each side or to desired degree of doneness. Spoon vegetables evenly onto individual serving plates; arrange steaks over vegetables.