Two ways to Brown the chicken tenders: Preheat a grill and season the chicken with salt and pepper, and then brown the chicken on the grill for 2 minutes per side. Remove and set aside. OR Heat 2 tablespoons of butter or oil in a large skillet over medium-high heat. Season chicken with salt and pepper and brown in skillet on both sides, about 2 minutes per side. Remove from skillet and set aside.
In a large skillet, heat one tablespoon of butter and sauté onion till soft and then add the garlic and let cook for one minute, just until you smell the garlic. Add the diced roasted red peppers and let cook for another minute.
Add the tomatoes and bring to a boil. Add the chicken back in the skillet and simmer for 25-30 minutes, or until chicken is tender and done.
When chicken is cooked through and tender, add the spinach and let cook for about 2 minutes.
If you prefer a non-paleo dish, you can serve over cooked pasta.