In a large skillet over medium-high heat, add ground beef and onion. Cook, until browned, breaking up beef with a wooden spoon, about 5 minutes. Drain well.
Meanwhile, core each tomato to remove the stem. Slice off 1/4-inch of the top of each tomato. Using a sharp paring knife or a small serrated knife, cut around the inside of the tomato to loosen the seeds and inner tomato pieces.
While holding the tomato over a bowl, use a small spoon to scoop out the seeds and inner tomato flesh. Dice any large inner tomato pieces and reserve, along with the seeds and juice.
Add tomato sauce, cooked rice, taco seasoning, and any reserved tomato pieces and juice to the skillet. Stir to combine and continue to cook until juices begin to thicken, about 10 minutes. Season to taste with salt and pepper.
Remove skillet from heat and cool filling slightly. Working with one tomato at a time, spoon beef filling into a tomato and mound carefully on top. Repeat with remaining tomatoes.
Serve your favorite toppings such as shredded cheese, sour cream, and thinly sliced scallions.
Video
Notes
Ground beef: For a lighter meal, substitute ground turkey or chicken.
Taco seasoning: To DIY a packet's worth of homemade taco seasoning, whisk together 1 Tbsp. chili powder, 1 1/2 tsp. ground cumin, 3/4 tsp. paprika, 1/2 tsp. ground coriander, 1/4 tsp. cayenne pepper, and salt to taste (I like 1/2 tsp.). Add 1 tsp. cornstarch if you prefer a thickener in your taco seasoning.
Yield: This recipe makes 8 hearty Stuffed Tomatoes burst with meaty taco flavors.
Storage: Store leftovers in an airtight container in the refrigerator for up to 4 days.