Combine the olives, parsley, pine nuts, lemon juice and salt and pepper in a medium bowl. Set aside.
Preheat a grill pan or the grill to medium-high heat. Mix the Harissa paste and the olive oil in a small bowl. Brush both sides of the bread lightly with the mixture. Grill the bread for about 1-2 minutes each side. Add the remaining Harissa and oil mixture to the olive mixture and stir to combine.
Top each slice of bread with the sliced heirloom tomatoes. Spoon over the olive mixture and top with the mint leaves. Makes 4.