Preheat the oven to 400° F. Spray the bottom and sides of an 8-inch x 8-inch baking dish with nonstick spray.
Layer ingredients in the dish:
Cut one bread slice in half and place the halves in the bottom of the dish. Cut another slice into strips and pieces, and fill in the gaps.
Layer half of the tomato slices over the bread, and then sprinkle ½ cup of the shredded cheese over the tomato.
Repeat with another layer of the remaining bread, tomato slices, and cheese.
Make the batter:
In a medium bowl, whisk together the eggs, milk, salt, garlic powder, onion powder, mustard, thyme, and pepper. Whisk until everything is well-combined.
Pour the egg mixture over the top over the layers in the baking dish.
Place the dish in the oven and bake the strata for about 35 minutes. It's done when the center no longer jiggles when the pan is gently shaken. Start checking the strata after about 30 minutes. If the top is browning too quickly, place a sheet of aluminum foil over the top.)
Move the pan to a cooling rack and let the strata cool for 10 minutes before slicing. Serve immediately.
Makes 6 servings. Leftover strata can be stored covered in the refrigerator for up to 3 days.
Notes
You can make this strata in advance: Assemble the layers, pour the egg mixture over, then wrap the dish and refrigerate it for up to 24 hours. Before baking, let the strata sit out at room temperature for about an hour.
Use the best quality tomatoes you can find in this dish since their flavor will be front and center in the strata. Heirloom tomatoes, with their exquisite shapes and colors, are great choices. Definitely take advantage of summertime garden tomatoes and farmer's market tomatoes when they become available.