Preheat your oven to 400°F. Place the cherry tomatoes on a baking sheet, drizzle with half the olive oil and a pinch of salt, and roast for 15 minutes until they burst and release their juices.
While the tomatoes roast, bring a small pot of salted water to a boil. Cook the penne according to package directions until al dente, then drain and set aside.
Season the chicken breast with sea salt and black pepper. Heat the remaining olive oil in a large skillet over medium-high heat and sear the chicken until golden and cooked through, about 5-6 minutes per side.
Remove the chicken from the skillet and let it rest for a few minutes before slicing it into bite-sized strips.
In the same skillet, add the diced onion and minced garlic, sautéing for 2-3 minutes until translucent and fragrant.
Add the roasted tomatoes (and all their juices), dried oregano, and fresh spinach to the skillet. Stir until the spinach is just wilted.
Return the sliced chicken and cooked penne to the skillet, tossing everything together to coat in the rustic tomato sauce.
Serve immediately topped with grated parmesan cheese and freshly torn basil leaves.