For the Basil Mayonnaise:
Make the Basil Mayonnaise: Combine mayonnaise and chopped fresh basil in a small bowl. Set aside.
Heat the grill to medium. Brush zucchini and/or yellow squash slices with olive oil and season with salt and pepper. Grill until squash is tender and has grill marks, about 3 minutes per side. Remove from the grill and set aside.
Brush bread with olive oil. Grill until golden brown and crisp, checking frequently and flipping halfway through. Remove the toast from the grill and rub each slice with the garlic clove.
Assemble the Smørrebrød: Transfer toasted bread to a clean work surface. Spread each slice with the Basil Mayonnaise. Top with a handful of arugula or lettuce leaves. Artfully arrange grilled zucchini and/or summer squash on top. Garnish with additional basil and/or microgreens if desired. Serve.
Calories: 402kcal | Carbohydrates: 40g | Protein: 9g | Fat: 23g | Saturated Fat: 4g | Cholesterol: 12mg | Sodium: 517mg | Potassium: 392mg | Fiber: 3g | Sugar: 5g | Vitamin A: 768IU | Vitamin C: 20mg | Calcium: 70mg | Iron: 3mg