Mash garlic and 1/2 teaspoon salt on a cutting board with the back of a fork until a paste forms.
Transfer to a medium bowl and whisk in lemon juice, cumin, paprika and pepper. Add chicken and stir to coat.
Heat oil in a large cast-iron pan over medium-high heat. Add onions and cook until golden brown, 6 to 8 minutes.
Using a slotted spoon, transfer the chicken to the pan (reserve the marinade) and cook, stirring occasionally until opaque on the outside, about 4 minutes.
Add chopped tomatoes with their juice, chickpeas, the reserved marinade and the remaining 1/4 teaspoon salt.
Reduce heat to medium and cook until the chicken is cooked through, 5 to 7 minutes more. Serve sprinkled coriander.