*Soak split peas in enough water to cover by 2 inches with 1 tablespoon salt for 8 to 12 hours in advance. This reduces cooking time and ensures they will soften if they've been stored a long time.
In a large pot, brown sausage in olive oil over medium heat. Remove sausage from pan and drain on a paper towel lined plate.
In the same pot, saute the onion, celery, and bell pepper in the rendered fat from the sausage until vegetables are softened and beginning to caramelize, 7-8 minutes (add more oil as needed). Add the garlic, salt and spices, cook another 2 minutes until the garlic is fragrant and the herbs release a pleasant aroma.
Add the carrots, zucchini, and split peas to the pot and pour in some of the chicken stock and stir to loosen any browned bits at the bottom to incorporate into the stew. Add the cooked sausage, remaining stock and Parmesan rind; bring to a boil. Reduce heat, cover and simmer for 45 minutes to 1 hour (if using lentils, simmer for 20 minutes), or until peas are tender. Add the tomatoes and cook uncovered for 30 minutes to meld flavors.
Stir in parsley just before serving. Remove Parmesan rind and serve with freshly grated Parmesan and crusty bread.
I use yellow split peas for soups like this because the color is so appealing. I tend to have better luck with bagged beans and split peas cooking evenly, rather than those kept in bulk bins.
Lentils can be substituted for the split peas, and will take less time to cook through (these seem to be okay from bulk bins). Any type lentil will work, though choosing red or yellow lentils will keep the soup bright in color. Brown or green lentils are just as delicious, but give the soup a muddy appearance.
Substitute hot Italian sausage or any link type sausage for all or part of the mild Italian sausage. If using precooked link sausage, slice into discs and brown in the same manner.