Slice zucchinis length-wise about a quarter inch thick. Brush pan lightly with olive oil. Heat stovetop grill on a medium to high flame. Grill zucchini slices, brown on each side (about 3-4 minutes). Remove from heat. Let cool.
Meanwhile, combine pesto and ricotta. Set aside. Toast or grill bread. Spread ricotta cheese mixture on cool toast. Top with two or three slices of grilled zucchini. Garnish with minced fennel fronds, scallion and a splash of lemon juice.