Charred Broccoli with Black Garlic Vinaigrette

Name: Charred Broccoli with Black Garlic Vinaigrette
Ingredients: 2/3 cup rice vinegar; 1/3 cup water; 1/2 ounce dried shiitake mushrooms (about 4 mushrooms) (from 1 [1-ounce] package); 1/4 cup black garlic cloves; 1 1/2 tablespoons light brown sugar; 1 1/2 teaspoons grated garlic (from 4 garlic cloves); 3/4 teaspoon kosher salt, plus more to taste; 1/4 cup grapeseed oil; 4 cups packed fresh broccoli florets (from 3 small heads broccoli [about 14 ounces]); 1/4 cup grapeseed oil, divided; Labneh or tzatziki (optional); 1 ounce feta cheese , crumbled (about 1/4 cup); 2 tablespoons salted roasted sunflower seed kernels