In a small bowl, mix together the taco seasoning ingredients. Set aside.
Wrap a ruler in foil, and hang it between two mugs, to create a tool for shaping the taco shells.
Place 1/2 cup shredded cheddar on a piece of parchment paper. Spread thinly into a 6-inch circle. Microwave on high until browned and crisp, about 2 minutes. Microwave ovens vary, so start checking after 1:30 minutes.
Allow the cheddar to cool no more than a couple of seconds, just until you can bear touching it. You want it to remain pliable. Gently peel it off the parchment paper, and fold it over the ruler (as illustrated in the photos above). This will shape the cheddar crisp into a taco shell.
Repeat three more times with the remaining cheese. Place the formed cheddar taco shells on plates.
Heat a large skillet over medium-high heat. Add the ground beef and the onion (you don't really need to add any fat, the meat will quickly render its fat). Cook, stirring to break up the meat, 2-3 minutes. Add the taco seasoning, the garlic and the tomato paste, and continue to cook until meat is cooked through, 2-3 more minutes.
Using a slotted spoon, scoop up the meat from the skillet, dividing it evenly among the cheddar taco shells. Add your choice of toppings (I used sour cream, guacamole and salsa) and serve.