Place the chicken gizzards in a slow cooker, along with garlic, onions and any aromatic ingredient a person wishes. Season them with pepper and salt; then add water, wine or chicken broth to cover them. Cook them in the slow cooker for 4 to 5 hours on a low setting until they are tender. Taste sample slices to keep them from being chewy. If an oven is used, cook for the same time at 275 to 300 degrees Fahrenheit.
To cook tenderized chicken gizzards, braise or confit them. If you wish to deep-fry or pan-sear gizzards, gizzards caramelize quickly in oil, and they are rarely tender after leaving the frying pan. The gizzards should be tenderized by soaking them in buttermilk for a day or two or by parboiling them for about 15 minutes. Use oil that has a high smoke point, such as vegetable oil or canola, when pan-searing the gizzards. When deep-frying them, dredge them in flour.
Barbecuing and baking converts tenderized gizzards into a melt-on-the-tongue appetizer. If a person chooses to bake the gizzards, cut them in half, season them with spices, herbs, salt and pepper, and then sprinkle olive oil. Bake for 25 to 30 minutes at 500 F.