Turn your Instant Pot to the "SAUTE" function and add a drizzle of olive oil to the inner pot. Add the lean ground beef, diced onion, seasoning salt, black pepper, and garlic powder. Break up the beef as it cooks until mostly browned.
Pour in 3/4 cup water. Use a wooden spoon or spatula to scrape up any flavorful browned bits from the bottom of the pot – this step is key to prevent a "BURN" message!
Gently sprinkle the brown rice evenly over the beef and water mixture. It's important not to stir the rice into the beef. Next, carefully layer the Worcestershire sauce, Dijon mustard, and the two cans of diced tomatoes over the rice, ensuring the rice is fully covered by the tomatoes.
Secure the Instant Pot lid, lock it in place, and move the knob to the sealing position. Cook on High Pressure for 10 minutes.
Once the cooking time is complete, allow the pressure to naturally release for 10 minutes. (If you're using white rice, immediately release the pressure after cooking). After 10 minutes, carefully turn the knob to vent any remaining pressure.
Open the lid. Gently mix the beef, rice, and tomato mixture with a fork. Sprinkle the shredded cheddar cheese evenly over the top, then place the lid back on for 2-3 minutes to allow the cheese to get perfectly melty.
While the casserole is cooking or melting, combine the light mayonnaise, Greek yogurt, ketchup, and a dash of salt and pepper in a small bowl. Whisk until smooth for your quick and creamy special sauce.
Dish out generous portions of the cheesy casserole. Serve with a dollop of the special sauce and a sprinkle of chopped dill pickles on the side. Enjoy your easy, healthy, and satisfying meal!