Prep the clams: If using canned clams, drain and reserve the clam juice. If using fresh clams, steam until they open; pick out the meat, and strain/reserve the cooking liquid.
In a large pot over medium heat, warm the olive oil. Add the diced bacon and cook until crisp, about 5 minutes.
Add the onion, celery, carrots, and green pepper. Cook, stirring often, until the vegetables begin to soften, about 5 minutes.
Stir in the garlic and cook just until fragrant, about 1 minute.
Pour in the reserved clam juice/broth and chicken broth, then add the crushed tomatoes, potatoes, bay leaves, thyme, and oregano. Bring to a boil.
Reduce heat to a gentle simmer (lid slightly ajar) and cook until the potatoes are fork-tender, about 15 minutes.
Add the clams and simmer gently for 5 minutes (avoid overcooking to keep clams tender).
Season with salt, black pepper, and (if using) red pepper flakes, Old Bay, and hot sauce. Remove and discard the bay leaves.
Ladle into bowls and top with chopped parsley. Serve hot.
Notes
Refrigerate leftovers in an airtight container for up to 3 days. To freeze, cool completely and store in freezer-safe containers (leave headspace) for up to 2 months. If you prefer a thicker chowder, simmer uncovered a few extra minutes.