Preheat the oven to 350°F and prepare the veggies. Slice potatoes into ~½ inch rounds, and then dice them into ½” cubes. Finely dice the white onion, bell pepper, and jalapeño, too.
Add the diced potatoes to the casserole dish and coat in olive oil and salt + pepper. Pop them into the oven for 25 minutes. We’re coming back to them, but potatoes need longer to cook. Next, make the fry sauce and prep the ground meat mixture.
For the fry sauce, combine all of the ingredients in a glass measuring cup or small bowl and stir. If you’d like, you can also add little pieces of diced pickle to the sauce for more texture. Store in the fridge until ready to use.
Heat a skillet to medium heat and grease with cooking spray. Add the lean ground beef, diced bell pepper, onion, and jalapeño. Mix until the ground beef is ~80% cooked, then mix in the Worcestershire sauce and ranch seasoning. Allow the beef to cook through.
By this time, the potatoes should be finished. Remove from the oven but keep the oven on. Add ground beef mixture, canned tomatoes (drained), and ½ of the fry sauce on top of the potatoes. Stir it all together.
Top the dish cheese, pickles, and sesame seeds. Cover the casserole with tinfoil sprayed with cooking spray (tinfoil is a must, otherwise it will significantly dry out). Bake for another 20 minutes.
Remove the tinfoil, serve with shredded lettuce and add remaining fry sauce. Enjoy!