Pat the chicken legs dry with paper towels.
In a small bowl, mix together kosher salt, black pepper, smoked paprika, garlic powder, onion powder, dried thyme, and dried oregano.
Rub the spice mixture evenly over all sides of the chicken legs.
Heat olive oil in a large skillet over medium-high heat.
Add the chicken legs skin-side down and sear for 3-4 minutes until golden brown. Flip and sear the other side for 2-3 minutes. Remove from heat.
Place the sliced onion and minced garlic in the bottom of the slow cooker.
Arrange the seared chicken legs on top of the onions and garlic.
Pour the chicken broth into the slow cooker around the chicken legs.
Cover and cook on LOW for 4 to 4 1/2 hours, or until the chicken is tender and the internal temperature reaches 165°F (74°C).
Carefully remove the chicken legs from the slow cooker and place on a serving platter.
Optional: To crisp the skin, place the chicken legs on a baking sheet and broil in the oven for 3-5 minutes until the skin is crispy and browned.
Serve hot with the cooked onions and pan juices spooned over the top.