Preheat oven to 400°F (204°C) and line a large baking sheet with parchment paper.
Arrange the garlic Texas toast slices on the baking sheet in a single layer. Bake for 8 minutes to partially cook the bread.
While the bread is baking, prepare the cheeseburger mixture.
In a large skillet over medium heat, cook the ground beef and diced onion, breaking the meat apart as it cooks, until browned and no longer pink. Drain excess grease.
Stir in yellow mustard, hamburger seasoning, and garlic powder. Cook for 2-3 more minutes, stirring occasionally, until well combined and heated through. Remove from heat.
Remove the bread from the oven. Gently press down the center of each slice with the back of a spoon or a small measuring cup to create a shallow well.
Spoon the beef mixture evenly into the wells of the garlic toast slices.
Sprinkle shredded sharp cheddar cheese evenly over the top of the beef.
Return the tray to the oven and bake for 8-10 minutes, or until the cheese is fully melted and bubbling.
While the bread is baking, in a medium bowl, whisk together sour cream, ketchup, red wine vinegar, mustard, and paprika until smooth. Set aside.
Once the garlic bread is out of the oven, drizzle each slice with the prepared burger sauce.
Top with finely diced dill pickles and cherry tomatoes.
Serve immediately.