To a medium bowl, add harissa paste, honey, olive oil, paprika, black pepper and juice from 1 lemon. Whisk ingredients to combine.
Use paper towels to pat boneless skinless chicken thighs dry. Use tip of knife to make small slits over the thick parts for marinade penetration. Season both sides with kosher salt. Place in the bowl with harissa mixture and turn to coat evenly. Cover bowl with plastic wrap or lid and refrigerate for 30 minutes.
Meanwhile, cut the remaining 3 lemons in half for grilling and preheat grill to 350°-375°F.
Grill chicken thighs for 4 minutes on each side. In the last 3 minutes of grilling, add the lemons and tomatoes to the grill.
Remove all foods from grill and allow to rest 5 minutes. Serve immediately with garnish of chopped cilantro and extra harissa paste on the side.