Place a large cast iron skillet over medium-high heat and add 1 tablespoon of extra virgin olive oil (EVOO).
When the oil is hot, add 1 pound of Italian sausage and break it apart with a spoon.
Brown the sausage until it is cooked through. When the sausage is finished cooking, spoon it onto a plate lined with a paper towel to absorb the excess oil.
Add the remaining 2-3 tablespoons of EVOO to the skillet with the sausage drippings. When the oil is hot, add 1 medium diced onion and sauté, scraping up the bits on the bottom of the skillet.
Add 2 medium russet potatoes and 1 large sweet potato, both cut into cubes, to the skillet. Season with flaky sea salt and freshly cracked black peppercorns to taste. Brown the potatoes on all sides.
Turn the heat to medium-low and place a tight-fitting lid over the skillet, continuing to cook for 15-20 minutes until the potatoes are tender.
Remove the lid and add 1 cup of diced zucchini, 1 chopped green bell pepper, and 2-3 chopped cloves of garlic to the skillet. Sauté everything together for 5-7 minutes until the vegetables are just tender.
Return the cooked sausage to the skillet and stir to combine. Taste and adjust seasoning with more salt and pepper if needed.
Serve hot, garnished with fresh herbs if desired.