Place the frozen fruit, 1/4 cup water, sugar and lemon zest in a small saucepan set over medium-high heat. Stir the cornstarch with 1 tablespoon of water in a small bowl and add to the saucepan. Bring to a boil, reduce heat, and simmer 2-3 minutes, until the sauce thickens.
Meanwhile, add the ricotta to a food processor and season with salt. Process until smooth and creamy.
Drizzle the olive oil over both sides of the whole-wheat toast and arrange the slices on a baking sheet. Sprinkle with sea salt.
Bake for 2-3 minutes on each side, until lightly browned.
Spread the whipped ricotta over the bread, and top with the banana berry sauce. Serve immediately.