Begin by heating 2 tablespoons of extra-virgin olive oil in a large skillet over medium heat. Once the oil shimmers, add one diced yellow onion and 2 cups of halved cherry tomatoes. Cook for about 7-8 minutes, stirring occasionally, until the onions become translucent and the tomatoes soften, releasing their juices into a jammy consistency.
Next, toss in 8 ounces of dry penne pasta along with 2 cups of marinara sauce and 2 cups of water. Season the mixture with 1 teaspoon of garlic powder, 1 teaspoon of dried oregano, and a pinch of kosher salt and cracked black pepper. Increase the heat to medium-high, bringing everything to a gentle simmer. Cover the skillet and let it cook, stirring occasionally, for about 10-12 minutes or until the pasta is al dente and has absorbed some of the sauce.
Remove the lid and lower the heat slightly. Stir in ½ cup of heavy cream, 4 cups of fresh baby spinach, and 1 cup of shredded mozzarella cheese. Cook for an additional 2 minutes, stirring frequently until the spinach wilts and the cheese melts into the creamy sauce.
For the final touch, remove the skillet from heat and garnish with a handful of chopped fresh basil leaves. If you’re feeling indulgent, sprinkle some grated Parmesan cheese over the top as well. Serve immediately and enjoy!