Sausage, Bell Pepper, and Onion Focaccia Sandwiches

In a large skillet sauté the bell peppers, the onions, the garlic paste, and the fennel seeds in the oil over moderately high heat, stirring, until the vegetables are browned lightly, cook the mixture over moderate heat, stirring, for 5 minutes, or until the vegetables are softened, and season the mixture with salt and pepper. While the vegetables are cooking, in a well-seasoned ridged grill pan or large skillet grill the sausage lengths over moderately high heat, turning them once, for 6 to 10 minutes, or until they are cooked through, and halve them lengthwise. Halve the focaccia squares horizontally, leaving one edge uncut to form a hinge, and fill them with the pepper mixture and the sausage.