Step 1
Preheat the oven's broiler and set the oven rack at about 6 inches from the heat source. Line a baking sheet with aluminum foil.
Step 2
Cut peppers in half from top to bottom; remove the stem seeds and ribs then place the peppers cut-sides down onto the prepared baking sheet.
Step 3
Cook peppers under the preheated broiler until the skin has blackened and blistered about 5 minutes.
Step 4
While peppers are cooking place portobello mushroom caps into a resealable plastic bag. Pour in balsamic vinaigrette squeeze out excess air and seal. Marinate in the refrigerator 8 hours to overnight.
Step 5
Remove blackened peppers from the oven transfer to a bowl and cover tightly with plastic wrap. Allow peppers to steam as they cool about 20 minutes. Once cool remove and discard skins. Refrigerate 8 hours to overnight.
Step 6
The following day preheat an electric double-sided grill (such as George Foreman®) according to manufacturers' directions. Sprinkle eggplant slices with garlic powder and onion powder.
Step 7
Remove portobello mushrooms from the marinade and discard the remaining marinade. Cook on the preheated grill until tender 4 to 5 minutes. Cook eggplant slices on the preheated grill until tender 4 to 5 minutes. Remove set onto a plate and sprinkle with Parmesan cheese. Set aside.
Step 8
To assemble the sandwiches spread all 8 slices of focaccia bread with a thin layer of ranch dressing. Layer 1/2 of the bread slices with a slice of Swiss cheese an eggplant slice a roasted pepper half a portobello mushroom cap and a slice of Asiago cheese. Top with the remaining bread.
Step 9
Spray the double-sided grill with cooking spray and cook the sandwiches until the cheese has melted the sandwiches are hot in the center and the bread is golden brown 4 to 5 minutes.