Heat 2 tbsp olive oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Dice your onion while the oil warms, then add it to the pan and stir for 2 minutes until it starts turning translucent. This is when you'll notice the sweetness emerge—that's your signal the onion is releasing its sugars, which builds the base flavor for the entire dish.

Add 3 minced garlic cloves to the onion and stir constantly for 30 seconds until the aroma fills your kitchen. I always hold my breath during this step because the smell is so concentrated it almost burns your nostrils, but that means the garlic is blooming correctly. If you let garlic brown instead of bloom, it turns bitter, so watch it closely and don't walk away.

Add your cubed chicken to the pan and cook for 4 minutes, stirring occasionally, until the outside is no longer pink. The chicken doesn't need to be cooked through yet—you're just sealing the exterior so it stays tender once the broth arrives. This step is where home cooks usually fail because they think the chicken needs to be fully cooked, but that leads to rubbery bites by the time everything finishes simmering.

Pour in 1 can of diced tomatoes with juice, 4 cups chicken broth, 1 tsp oregano, 1 tsp basil, and 1/2 tsp red pepper flakes. Increase heat to high and bring everything to a boil—this takes about 3 minutes. Once you see aggressive bubbles breaking the surface, you know the temperature is right for adding pasta.

Add the 12 oz penne directly into the boiling broth and stir well so no noodles stick to each other or the bottom. Reduce heat to medium and let it simmer for 18-20 minutes, stirring every 4 minutes. The pasta will seem underdone at minute 15, but keep trusting the process because it's absorbing all that broth and becoming part of the one pot pasta crowd summer magic.

Add 1 cup fresh spinach and stir until it wilts into the hot pasta, about 1 minute. The spinach will turn dark green and seem to disappear, but it's still there—folded into every bite. This is my favorite step because everything rages-to-life-green just before you finish.

Remove from heat and top with 1 cup shredded mozzarella and 1/2 cup grated Parmesan. Stir gently until the cheeses melt completely and coat the noodles. The Parmesan creates a sharp edge against the creamy mozzarella, so both cheeses matter here—never skip one for the other.