• Roast the chiles over an open flame–on the grill or stovetop or under broiler–on high heat. Turn the peppers occasionally, until blistered and blackened on all surfaces, 3 to 5 minutes on each exposed side. Place in a covered dish or in a plastic bag and set aside to cool. After about 10 minutes, peel away the blackened skin and remove the seeds. Set aside.
• Heat the olive oil in a skillet and cook the onions until it is transparent. Add the diced squash and cook a few more minutes. Season to taste with salt.
• In a bowl, mash the potatoes, adding a bit of liquid if needed. Mix in the onion and zucchini along with the diced cheese. Season to taste with salt and freshly ground pepper. 

Make the sauce:

• Puree the tomatoes, onion and garlic in a blender. Heat the oil in a skillet and add the tomato mixture. Cook, stirring occasionally. If using the broth powder, stir it into the sauce and cook a few more minutes.

Assemble and bake:

• Heat the oven to 350 degrees F. Stuff the peeled peppers with the potato mixture. Spread tomato sauce in the bottom of a shallow casserole dish. Lay the stuffed chiles in the sauce. Cover and cook until the sauce is bubbling and the cheese has melted, about 15 minutes. Drizzle with crema, sour cream, or whole milk yogurt.