If you don't want to make a batch of my Mexican mole spice blend, use 1 tablespoon cumin, 1 tablespoon unsweetened cocoa, 2 teaspoons +/- ancho or other red chile powder, and 2 teaspoons cinnamon.
When cooking in an Instant Pot, flours can cause a "burn" error. I like a fairly thick chili, and I've successfully used 1/3 cup masa. However, to be safe, I recommend starting with 2 tablespoons. Stir it in well both while it browns and when you add the liquid. If when you de-pressurize you want it thicker, sprinkle more masa and stir it in a little at a time on the saute setting. The chili must come to a boil for thickener to do its job.
If "lean" ground lamb is a question mark, on this recipe it's not an issue. I have 2 markets that I get ground lamb from. The amount of white fat to red meat is a good sign that it is lean. Additionally, I don't have much (if any) grease in the pan after browning. You can certainly remove excess.
I typically don't add salt to beans until after cooking as I think it messes with liquid absorption. Don't forget to season before serving!
Macronutrients are an approximation only from MyFitnessPal.com and use 14 ounces ground lamb and 2 tablespoons masa harina. I did not include toppings.