Heat 8- or 10-inch nonstick skillet over medium-high heat. Cook bell peppers, onion and dressing in skillet 4 to 5 minutes, stirring occasionally, until peppers are crisp-tender; remove from heat.
Cut focaccia into 2 wedges; split each wedge horizontally. Spoon half of the vegetable mixture onto each bottom wedge; sprinkle with basil and cheese. Top with tomato and tops of bread wedges.