Prepare the Sauce: In a bowl, whisk together tahini, water, 2 tablespoons lemon juice, and garlic until smooth. Season with salt and pepper. (Sauce can be refrigerated for up to 4 days; bring to room temperature before using.)
Make the Meatballs: In a bowl, mash ¼ cup of the prepared sauce with panko bread crumbs to form a paste. Add ground lamb, 2 tablespoons mint, ½ teaspoon cinnamon, ½ teaspoon cumin, and ½ teaspoon salt. Knead until combined, then roll into 12 meatballs (about 1½ inches each).
Sauté Aromatics: Set the pressure cooker to the highest sauté function. Heat oil until shimmering, then add onion and remaining ¼ teaspoon salt. Cook for about 5 minutes until softened. Stir in the remaining ½ teaspoon cinnamon, remaining ½ teaspoon cumin, and cayenne. Cook for 30 seconds until fragrant.
Cook the Meatballs: Pour in the chicken broth, scraping up browned bits. Add the meatballs, lock the lid, and select high-pressure cooking for 1 minute.
Steam Release & Prepare Couscous: Quick-release pressure and remove the lid carefully. Use a slotted spoon to transfer meatballs to a plate and cover with foil. Ensure there are 2 cups of cooking liquid remaining in the pot (add extra broth if needed).
Cook Couscous: Bring liquid to a simmer using the sauté function. Stir in couscous, roasted red peppers, lemon zest, and remaining 1 tablespoon lemon juice. Turn off heat, cover, and let sit for 10 minutes.
Serve: Fluff couscous with a fork and transfer to a serving dish. Arrange meatballs on top, drizzle with remaining tahini sauce, and sprinkle with pickled onions and remaining mint. Serve immediately.