Bring a large pot of water to a boil and season generously with salt. Add penne and cook until al dente, about 10 minutes. Drain, reserving ½ cup pasta water.
Heat a large heavy-duty pot over medium-low. Add pancetta and cook until fat has rendered and pork begins to caramelize, 10 minutes. Transfer to a bowl using a slotted spoon; reserve drippings in pot.
In a medium bowl, toss shrimp with Homemade Cajun Seasoning.
Add shrimp to pot and cook until just cooked through, turning once or twice, about 3–4 minutes. Remove and transfer to bowl with pancetta.
Add butter to pot; once melted, stir in onions and garlic; season lightly with salt. Cook until onions begin to soften, about 5 minutes. Add tomatoes and cook until liquid evaporates, about 2 minutes. Stir in the wine and cook until liquid is reduced, about 2 minutes longer. Stir in chicken broth and heavy cream and bring to a simmer.
Fold in cooked pasta, pancetta, and shrimp. Taste and season with salt and pepper, adding pasta water as necessary to coat the noodles.
Remove from heat and gently stir in thyme, oregano, and lemon juice. Serve hot with grated parmesan cheese.