Prepare the grill for direct grilling over a medium fire (about 400°F).
Insert a toothpick into the side of the onion slice to keep the rings together while grilling. Brush with olive oil and sprinkle with sea salt. Very lightly brush the eggplant slices with olive oil and sprinkle with sea salt.
Grill the onion over direct heat for about 12 minutes, turning occasionally until softened. Grill the eggplant slices over direct heat for about 8 minutes, turning once until tender.
Remove the onion and eggplant slices from the grill. Stir couscous into boiling chicken stock.
Return to a boil and reduce heat to a simmer. Stir occasionally, uncovered, until the couscous is somewhere between al dente and tender. Add more chicken stock along the way as needed.
While the couscous is cooking, dice the eggplant and onion slices. Strain/drain the couscous and place in a medium bowl.
Stir in 1 teaspoon olive oil, 1 teaspoon lemon juice, 1/4 teaspoon salt and the cilantro. Fold in the eggplant and onion, being careful not to break up the eggplant.
Adjust seasoning as needed with salt or cilantro. Serve warm as a side or cold as a salad.
