Savory Vegan Breakfast Sandwiches

Ingredients

• ¼ cup apple cider vinegar
• 3 tablespoons Bragg Liquid Aminos or soy sauce
• ¼ cup olive oil
• 1½ teaspoons black pepper (divided)
• 1 14-ounce package firm tofu (drained and cut crosswise into 8 slices)
• 1 large onion (chopped)
• 4 cloves garlic (chopped)
• 8 ounces button mushrooms (sliced)
• 1 medium tomato (chopped)
• 2 cups baby spinach leaves
• ½ teaspoon dried thyme
• 1 teaspoon salt
• vegan butter (such as Earth Balance (optional))
• 4 English muffins (toasted)