28 ounces crushed tomatoes — some of the sauce drained
2 tablespoons tomato paste
2 cups grated cauliflower — about 1/2 pound
2 teaspoons dried oregano
1 teaspoon dried thyme
1 cup sliced olives
3 tablespoons chopped fresh parsley
4 large sweet bell peppers
1/3 cup shelled pistachios — coarsely chopped just enough to create jagged edges
Sea salt and freshly ground pepper
Heat oven to 375°F. Heat 2 tablespoons of olive oil in a large skillet over medium heat, spreading the oil evenly over the pan. Add the sliced onions and stir to coat the onions with the oil. Continue to cook onions over medium heat, about 10 minutes, stirring occasionally. Season with 1/2 teaspoon of salt and spread onions out evenly in the skillet, reduce heat to low. Allow onions to caramelize, stirring occasionally, while preparing the rest of the dish, about 35 minutes.
In another skillet, brown the sausage, breaking up into bite-size pieces as it cooks. Transfer to a plate and set aside. In the same skillet, cook the carrots and mushrooms in the rendered fat over medium heat 5 to 6 minutes. Stir-in the garlic, tomatoes, and tomato paste; cook for 2 more minutes.
Add the grated cauliflower to the skillet with the oregano and thyme; cook for 2 minutes, then transfer to a large bowl. Salt and pepper, to taste. Remove the onions from the skillet and set aside 2/3 cup for topping. Chop the remaining onions and toss with the cauliflower mixture, sausage, olives, and parsley until well combined.
Slice the bell peppers in half and remove seeds. Brush the outside of the peppers with a thin coat of olive oil and lightly season the inside with salt and pepper. Fill the peppers with the stuffing and sprinkle with pistachios. Pour 1/4 cup of water in the bottom of the pan and bake for 20 minutes. Remove from the oven and top with the caramelized onions, as desired. Continue to bake an additional 20 to 25 minutes, or until peppers are tender and onions are golden brown.
The caramelized onions and stuffing can be made and mixed days in advance. Peppers can be stuffed up to 24 hours in advance.