Instant Pot Beef & Poblano Tostadas

Season beef on all sides with onion powder, garlic powder, black pepper, and 1/2 teaspoon salt. Add oil to a programmable pressure multicooker (such as Instant Pot). Select SAUTE on cooker. Select HIGH temperature setting, and allow to preheat. Add beef; cook, turning occasionally, until golden brown on all sides, about 15 minutes. Transfer beef to a heatproof bowl. Add poblano chiles and onion to cooker; cook, stirring often, until vegetables slightly soften, 3 to 4 minutes. Add 1/2 cup of the vinegar, stirring to scrape up any browned bits from bottom of cooker.

Return beef to cooker. Press CANCEL. Cover cooker with lid; lock in place. Turn steam release handle to SEALING position. Select MANUAL/PRESSURE COOK setting. Select HIGH pressure for 65 minutes. (It will take 10 minutes for cooker to come up to pressure before cooking begins.)

Carefully turn steam release handle to VENTING position, and let steam fully escape. (This will take 3 to 4 minutes.) Remove lid from cooker. Transfer beef to a clean heatproof bowl; let cool 10 minutes.

Whisk together cornstarch and cold water in a bowl until combined. Select SAUTE setting on cooker. Select HIGH temperature setting, and let liquid in cooker come to a boil. Add cornstarch mixture, whisking until combined. Cook, whisking often, until mixture thickens, about 1 minute. Turn cooker off. Shred beef; add to liquid in cooker, and stir to coat.

Toss together cabbage and bell peppers in a bowl. Whisk together mayonnaise, 2 tablespoons vinegar, and 1/4 teaspoon salt in a bowl. Add to cabbage mixture; toss to coat. Using a slotted spoon, spoon beef mixture onto tostadas; top with slaw and cilantro. Serve with lime wedges, if desired.