Wash and cut the tomatoes in half horizontally. Scoop out the seeds and seeds membrane and set aside.
Place half of the avocado in a bowl and mash with a fork until almost smooth. Add yogurt, mayo, lime juice and cumin and stir to combine. Dice remaining half of the avocado and add it alongside ¼ teaspoon salt. Stir gently to combine. Set aside.
In a bowl, season ground beef with ½ teaspoon of salt, black pepper and chili powder and mix well. Divide into equal 4 portions and gently shape each portion into ½-inch thick patty. Preheat grill (or grill pan) to medium-high heat. Grill patties 3 minutes on each side or until desired degree of doneness.
In the meantime, lightly grease with olive oil a medium non-stick pan or skillet and heat over medium-high heat. Cook halved tomatoes face down for 2 to 3 minutes, until they begin to brown. Flip and cook for 20 seconds on the other side so that they get a bit of color.
To assemble burgers, place a large pinch of sprouts on the bottom part of each tomato, top with a beef patty, add a generous swipe of Honey Dijon mustard to the patty and about 2 tablespoons of avocado sauce. Finish with the other half of each tomato.
Looking for the ideal pairing? Ask our Mustard Sommelier by tweeting him at #AskMaille