Cut the Chuck Roast into 1 1/2 -2 inch steaks so we can brown half of them to help develop flavor. Season the steaks generously with salt and pepper and set aside.
Cut the ends off of the zucchini and slice them lengthwise into 1/2 inch thick slices. Toss them with EVOO, Salt and Pepper and put them on a rimmed baking sheet lined with parchment paper. Set this aside.
Put the dried, destemmed and deseeded chilies on a microwave safe plate and heat them in the microwave in 10 second increments until fragrant and pliable- about 30 seconds total.
Put the chilies, chipotles, and chicken stock in a 2 quart microwave safe bowl or measuring cup. Cover with BPA-free plastic wrap and heat in microwave until gently simmering- about 5 minutes. Set aside.
Use the saute function on the InstantPot and add the cooking fat once it starts to heat up. We're going to brown half of the chuck roast steaks so we don't want to over crowd the pot. We'll turn the steaks over after 5 minutes. Once we've browned half of the steaks and removed them to a cutting board, add the ground pork and brown it and then remove it to a bowl.
Add the onions and brown them until softened, about 2 minutes. Add the garlic, cinnamon, cumin, coco, allspice and oregano and stir constantly until fragrant about 1 minute. Add the dried chilies and chicken broth to the InstantPot and then pour all of these ingredients into the jar of a heavy duty blender. IMPORTANT NOTE- you DON'T want to blast this on high or you're going to get a scalding facial. Put a clean dish towel over the lid of the blender and start the blender at the lowest speed possible. Blend until smooth. Return the pureed ingredients to the InstantPot
Cut the Chuck Roast into 1-2" chunks and add those and the pork to the InstantPot. Gently season with salt and pepper. Seal the vent and set the InstantPot to Pressure (High) for 30 minutes.
Pre-heat the oven to 400 degrees for the zucchini.
When time is up on the InstantPot this is a good time to put the zucchini in the oven and then carefully release the pressure on the InstantPot. And remove the lid. Stir in the vinegar, the fish sauce and a slurry of the masa harina and a small amount of water. Simmer the chili until thickened- about 5-10 minutes. Check on the zucchini and add cheese and return to oven for 5 minutes for cheese to melt.
Serve the chili and garnish with desired toppings.