Heat the 1-3/4 cups of vegetable stock to boiling in a small sauce pan. Add the rice and stir. Return to boil and cover. Reduce heat and simmer for 35 - 45 minutes. Stock should be absorbed and rice should be fairly tender. Cool slightly and place in a large bowl.
Quarter the zucchini lengthwise and slice thinly. Coarsely chop onion and mushrooms. Set aside with the minced garlic.
Heat a medium fry pan and add the olive oil. Swirl to cover the bottom of the pan. Add the onion and cook and stir for about 3 minutes. Add the mushrooms and cook and stir for 2 minutes more.
Add the zucchini and garlic to the pan and cook for 4 minutes or so. The vegetables should be slightly soft and just beginning to brown. Remove from the heat and add to the rice in the bowl.
Slice the tomatoes into small pieces and add to the bowl.
Roughly chop or crumble the meatloaf and add to the bowl. If you are using another protein, chop it into small bite-sized pieces. Add to the bowl. Stir the ingredients to mix. Add the 1/2 cup of stock and stir once more. Cover and refrigerate for at least 1 hour.
Slice the peppers in half lengthwise. Remove the seeds and white membranes. Spray a medium casserole with non-stick spray. Place the pepper halves in the pan cut side up. Preheat the oven to 375 degrees.
Divide the mixture between the 4 pepper halves, packing lightly. Spoon approximately 1 tablespoon of the marinara on top of each filled pepper. Cover tightly with foil and place in the oven. Bake for 35 minutes.
Remove the pan from the oven and remove the foil. Add another tablespoon or so of the marinara to each pepper and sprinkle with the cheese. Spoon any remaining marinara into the pan to coat the bottom,
Return the pan to the oven uncovered and bake for 10 - 15 minutes until the cheese is melted and the peppers are a little brown. Serve.
Wipe the mushrooms clean with a damp cloth. Slice 1/4 inch thick. Set aside.
Heat olive oil in a large skillet and add the onion and garlic. Saute until the onion is softened and the garlic is fragrant, 3-4 minutes.
Add the vinegar, brown sugar, lemon pepper and tarragon. Simmer mixture for a few minutes. Add the mushrooms and continue to cook 7-10 minutes, stirring frequently. The liquid should reduce and thicken slightly.
Put in a glass jar or zip top bag and refrigerate overnight or for up to 3 days. Serve as part of a relish tray, on a salad, or as a side dish.