Combine marinade and pesto in a large Ziplock bag then add chicken breasts and squish to coat. Marinade in the refrigerator for at least 30 minutes, or up to 8 hours.
Saute marinated chicken in a large skillet sprayed well with non-stick spray over medium heat for 5-6 minutes a side, or until no longer pink in the center. Remove to a plate then cover loosely with foil to stay warm and set aside. Carefully wipe out skillet with a spatula or wet paper towel. Meanwhile, bring a large pot of water to a boil then season with salt and add penne. Cook until al dente then drain and set aside.
Still over medium heat, add oil to the skillet then add onions and season with salt and pepper. Saute for 3-4 minutes, or until tender, then add garlic and saute, stirring constantly, for 30 more seconds. Carefully add chicken broth then let simmer until reduced by half, about 2 minutes. Add tomato sauce and evaporated milk then whisk in flour and pesto. Simmer until thick and bubbly, about 2-3 minutes. Add cooked and drained pasta then toss to combine. Portion out to plates then top with cooked chicken.