Preheat the oven to 400°F (200°C). Arrange a 9 x 13-inch baking dish and set aside a medium bowl and a large skillet.
Trim the stem ends from the bell peppers and remove seeds to make bowls, then place the peppers upright in the prepared baking dish.
Dice the zucchini and put it in the medium bowl. Sprinkle with 1 teaspoon salt, toss, and let the zucchini sit 10–15 minutes to release moisture.
Heat the skillet over medium-high heat. Add the ground beef, chopped onion, minced garlic, Italian seasoning, cumin, and chili powder. Season with salt and pepper and cook, breaking up the meat with a wooden spoon, until browned and crumbled, about 5–10 minutes.
While the meat cooks, drain most of the liquid from the zucchini by pouring off juices and pressing with paper towels until mostly dry.
Cut the cream cheese block into six equal pieces and place one piece into the bottom of each pepper, pressing it into an even layer.
Spoon 3–4 tablespoons of the drained diced zucchini into each pepper over the cream cheese layer.
Distribute the cooked ground beef mixture among the six peppers, using about 1/4 to 1/3 cup per pepper and filling to the top.
Spoon about 2 tablespoons of crushed tomatoes on top of each stuffed pepper.
Bake the peppers at 400°F for 30 minutes, then remove them from the oven.
Sprinkle approximately 2 tablespoons shredded cheddar over each pepper and return to the oven for 5 more minutes, until the cheese melts.
Remove from the oven, garnish with chopped scallions if using, and serve warm.