1. Heat oil in a small non-stick skillet on medium high heat. Add onions and stir. Saute for 2 minutes. Stir in mushrooms and salt and pepper to taste. Saute for 5 minutes or until onions are soft and golden brown and mushrooms have released most of their moisture. Add spinach and garlic and mix in. Cook for another 2 minutes.
2. Add cubed bread into a large bowl. Mix in cooked veggies and set aside.
3. In a medium bowl, whisk together eggs, milk, chives, dried basil, red chili flakes and salt and pepper to taste.
4. Butter a 8x8 baking pan. Add half the bread and veggies mixture to the pan and spread evenly. Sprinkle half the cheddar cheese on top and pour the egg mixture over the entire pan. Use a spatula to press th bread down into the liquid. Top with the rest of the bread nad veggies mixture and the rest of the cheese. Press down on the bread with a spatula a few times to make sure all the bread can soak up the liquid. Set aside for 30 minutes or overnight.
5. Pre-heat oven to 355 F. Bake the strata for 40-50 minutes. The cheddar cheese sould be nice and bubbly and golden brown!
6. While the strata is baking, mix all the ingredients for the heirloom cherry tomato salad in a small bowl with some salt and pepper to taste.
7. Serve strata while hot with a generous serving of the heirloom tomato salad! Enjoy!