"One of my husband's and son's favorites is Mongolian beef from that popular Chinese-American restaurant chain... I thought I'd surprise them and whip up an Instant Pot® recipe of their favorite dish... it got a rating of approval from them. Serve over rice."
Preheat the oven to 350 degrees F (175 degrees C).
Brush unpeeled garlic cloves with a small amount of olive oil and wrap in a piece of aluminum foil.
Bake in the preheated oven until garlic cloves are tender and browned, about 20 minutes. Let cool; remove skin from cloves.
Season steak with salt and pepper. Add oil to a multi-functional pressure cooker (such as Instant Pot(R)) and select Saute function. Cook steak in batches until browned, about 8 minutes. Do not crowd the pot. Transfer beef to a plate.
Saute garlic in the pot until fragrant, about 1 minute. Add onions, brown sugar, 1/2 cup water, green bell pepper, red bell pepper, liquid aminos, and ginger. Stir to combine. Add browned beef and any accumulated juices.
Close and lock the lid. Select high pressure according to manufacturer's instructions; set timer for 12 minutes. Allow 10 to 15 minutes for pressure to build.
Release pressure carefully using the quick-release method according to manufacturer's instructions, about 5 minutes. Unlock and remove the lid.
Combine 3 tablespoons water and arrowroot powder in a bowl; whisk until smooth. Add mixture to the sauce in the pot, stirring constantly. Select Simmer mode and bring to a boil; stir constantly until sauce thickens, about 5 minutes. Stir in green onions.