Preheat your oven to 325°F / 165°C. Lightly grease a 2-quart or 8x8-inch square baking dish.
In an extra-large bowl, combine the bread cubes, drained tomatoes, thawed spinach, Italian cheese blend, chopped onion, kalamata olives, and minced garlic.
Toss gently until everything is well mixed, then transfer the mixture to your prepared baking dish.
In a separate large bowl, whisk together the eggs, half-and-half, and crushed red pepper until smooth.
Pour this custard mixture evenly over the bread in the baking dish. Use the back of a spoon to gently press down on the bread, ensuring it soaks up the liquid.
Don't worry if the dish looks very full!
Bake uncovered for 60 to 65 minutes. The strata is ready when it's beautifully puffed, golden brown, and a thermometer inserted into the center registers 170°F / 77°C.
Let the strata stand for 15 minutes before slicing and serving to allow it to set properly.