Bring a large pot of salted water to a boil. Add the 8 oz of penne pasta and cook according to package instructions until al dente, usually about 10-12 minutes. Drain the pasta and set aside, reserving about 1/2 cup of pasta water to loosen the sauce if needed.
Heat 2 tablespoons of olive oil in a large skillet over medium-high heat. Add the bite-sized chicken pieces, seasoning them with salt and pepper. Cook for 5-7 minutes, stirring occasionally, until the chicken is golden brown and cooked through. Remove the chicken from the pan and set aside.
In the same skillet, reduce the heat to medium. Add the minced garlic and sauté for about 1 minute until fragrant but not burnt. Toss in the halved cherry tomatoes and cook for 2-3 minutes until they start to soften. Add the fresh spinach and cook until wilted, about 1-2 minutes.
Pour in 1 cup of heavy cream and stir to combine with the garlic and vegetables. Bring the mixture to a gentle simmer, then add 1/2 cup grated Parmesan cheese. Stir continuously until the cheese melts and the sauce thickens slightly. Season with salt, pepper, and red pepper flakes if using.
Return the cooked chicken to the skillet and stir to coat with the sauce. Add the drained penne pasta and toss everything together. If the sauce is too thick, add a splash of the reserved pasta water to loosen it. Garnish with fresh basil leaves before serving.