To veganize, omit sausage and cheese

“Enhanced by sausage and cheese, this ratatouille makes a complete meal. For vegetarians, just omit the sausage. (Recipe contest entry: Mrs. Gene Stecyk, Los Angeles, CA)”—The Garlic Lovers’ Cookbook (1980) 
GILROY RATATOUILLE  
Makes 8 servings 

5 cloves fresh garlic, minced 
2 onions, sliced thin 
1/3 C olive oil 
1 bell pepper, cut into thin rounds 
2 medium eggplant, unpeeled, diced 
2 medium zucchini, sliced ¼-inch thick 
20 oz Italian plum tomatoes (can use stewed, preferably homemade—see recipes in Basics and Canning … sections—or canned) 
1 ½ tsp basil 
1 ½ tsp parsley 
1 ½ tsp salt 
Fresh ground pepper to taste 
1 ½ lbs Italian sausage, cooked until done, drained well (preferably homemade—see recipes in Meats section) 
½ lb whole small mushrooms 
1 C (4 oz) grated Swiss cheese 

Sauté garlic and onions in olive oil until soft, add bell pepper, eggplant, and zucchini, and cook 5 minutes over medium heat, tossing well. Add tomatoes with liquid, basil, parsley, salt, and pepper, simmer uncovered for 15 minutes, then cover and simmer 15 minutes longer. Add mushrooms to vegetables during the last 10 minutes of cooking time. Add drained sausage to vegetables, sprinkle with grated cheese, cover, and simmer until cheese melts.