Preheat the oven to 375℉/190℃ and grab a casserole dish or another oven-safe dish that is long enough to hold spaghetti.
Add half a cup of the tomato sauce to the bottom of your baking dish. Then place the pasta on top. Next, pour the broth on top and gently mix to get the liquid in between your noodles to prevent sticking.
Top with all the remaining ingredients: onion, garlic, spinach, sundried tomatoes, oregano, salt, pepper, and the remaining sauce.
Bake uncovered for 30 minutes. Then gently stir/mix and continue baking for another 15 minutes, or until desired doneness is reached.
Notes
Bake your dish until the pasta is 'al dente' for the best texture. Do not overbake. Al dente means that the pasta is still firm once cooked, giving optimal texture in every bite.