In food processor, blend olives, herbs, and garlic. With processor running, slowly drizzle in 2/3 cup oil. Blend until olives are finely chopped; season. Halve the hearts of palm lengthwise; pat dry with paper towels. Heat remaining 2 tbsp. oil in grill pan over medium-high. Add hearts of palm and cook, working in batches if needed, until warmed through, about 3 minutes per side; transfer to a plate. Add lemon to pan, cut-side down. Cook until grill marks form, about 2 minutes. Spread some tapenade on a platter and arrange hearts of palm on top. Drizzle with remaining tapenade and sprinkle with parsley. Serve with grilled lemon.