Spring Vegetable Soup with Ricotta Toast

Name: Spring Vegetable Soup with Ricotta Toast
Ingredients: 1/4 cup extra-virgin olive oil, plus more for drizzling; 12 ounces oyster mushrooms, sliced if large; Kosher salt and freshly ground pepper; 5 cloves garlic (4 thinly sliced, 1 lightly smashed); 3 leeks, halved lengthwise, well rinsed and thinly sliced; 4 cups low-sodium chicken broth; 1 sprig rosemary; 4 1-inch-thick slices ciabatta bread; 1/2 cup part-skim ricotta cheese; 1 teaspoon finely grated lemon zest; 1 cup frozen peas, thawed; Shredded pecorino cheese, for sprinkling