Italian tuna melt

Ingredients

• 3 tbsp extra-virgin olive oil , divided
• 2 tbsp lemon juice , divided
• 1/4 tsp salt
• 2 170-g cans chunk light tuna , in water (drained)
• 1/2 398-mL can artichokes , drained and cut into small wedges
• 1/4 thinly sliced red onion
• 2 cups arugula
• 4 large slices Italian bread , on a large baking sheet
• 1/2 cup grated mozzarella