Whisk all Tahini sauce ingredients in bowl until smooth (mixture will appear broken at first). Season with salt and pepper to taste. Let sit at room temperature for at least 30 minutes to allow flavors to meld. (Sauce can be refrigerated for up to 4 days; bring to room temperature before serving.)
Microwave vinegar, sugar, and salt in medium bowl until simmering, 1 to 2 minutes. Add onion and let sit, stirring occasionally, for 45 minutes. Drain onion and return to now-empty bowl. (Drained onions can be refrigerated for up to 1 week.)
Using fork, mash 1/4 cup Tahini Sauce and panko together in bowl to form paste. Add ground lamb, 2 tablespoons mint, 1/2 teaspoon cinnamon, 1/2 teaspoon cumin, and 1/2 teaspoon salt, and knead with hands until thoroughly combined. Pinch off and roll mixture into twelve 1 1/2 inch meatballs.
Using highest Sauté function, heat oil in Instant Pot until shimmering. Add onion and remaining 1/4 teaspoon salt and cook until onion is softened, about 5 minutes. Stir in remaining 1/2 teaspoon cinnamon, remaining 1/2 teaspoon cumin, and cayenne and cook until fragrant, about 30 seconds. Stir in broth, scraping up any browned bits. Add meatballs to pot. Lock lid in place and close pressure release valve. Select Pressure Cook function and cook for 1 minute.
Turn off Instant Pot and quick-release pressure. Carefully remove lid, allowing steam to escape away from you. Using slotted spoon, transfer meatballs to plate, tent with aluminum foil, and let rest while cooking couscous. (You should have about 2 cups cooking liquid remaining in pot; add extra broth as needed to equal 2 cups.)
Using highest Sauté function, bring liquid in pot to simmer. Stir in couscous, red peppers, and lemon zest and juice. Turn off Instant Pot, cover, and let sit for 10 minutes. Fluff couscous gently with fork and transfer to serving dish. Arrange meatballs on top and drizzle with remaining 1/4 cup Tahini Sauce. Sprinkle with pickled onions and remaining 2 tablespoons mint. Serve.
Notes
*Pressure Cook and Manual buttons are interchangeable