Preheat broiler to high.

Warm olive oil in a large, nonstick skillet over medium-high heat. Add the sliced squash, toss in the olive oil, and cook for 1 minute. Carefully add 1 tablespoon water, cover, and cook until the squash is tender (about 3 minutes). Stir the squash a few times to keep it from burning. Add rosemary, lemon zest, a pinch of salt and several turns of black pepper, stirring to combine. Season to taste with additional salt and pepper, then take the skillet off the heat.

Lightly brush the top of each baguette slice with olive oil, then toast under the broiler until golden. While the bread is still hot, rub the surface with garlic (one of my favorite smells). Spread the ricotta evenly over each of the baguette slices. Top with slices of sautéed squash. Finish with a sprinkling of flaky sea salt and a little more black pepper.