Preheat your oven to 450°F.
Bring a large pot of water to a boil and cook the penne pasta according to package instructions. Before draining, reserve ¼ cup of the starchy pasta water. Then drain the remaining water and set the pasta aside.
Place the frozen salmon and fresh cherry tomatoes on a large, rimmed baking sheet. Drizzle with 2 tablespoons of extra virgin olive oil and season generously with kosher salt and black pepper.
Roast at 450°F for 20-25 minutes. If the tomatoes cook faster than the salmon, carefully remove them from the pan and set them aside. I like to start checking on the tomatoes around the 15-minute mark. Continue roasting the salmon until it flakes easily with a fork and reaches an internal temperature of at least 145°F. The salmon should be opaque and cooked through.
While the pasta, salmon, and cherry tomatoes cook, prepare the butter garlic sauce. Melt the butter in a large skillet over medium heat. Add the diced onion and minced garlic, then sauté for about 3 minutes, until the onion is soft and the garlic is fragrant.
Add the white wine and continue cooking the sauce at a strong simmer for about 1 minute.
Add the Dijon mustard, reserved pasta water, and ¼ teaspoon of ground black pepper. Stir and cook for another minute.
Stir in the fresh lemon juice and remove the sauce from the heat.
Once the salmon is fully cooked (and has reached an internal temperature of at least 145°F), use a fork to gently flake it into bite-sized pieces. Add the flaked salmon to the butter-garlic sauce and stir to coat so it can soak up some of the rich, buttery flavors.
Pour the sauce and salmon mixture over the cooked pasta and toss until well combined. Finally, gently fold in the roasted cherry tomatoes.
I like to finish the pasta with plenty of freshly grated Parmesan cheese and a sprinkle of fresh parsley or fresh basil. Serve right away while the pasta is warm.