Spread 1 teaspoon coconut oil into the bottom of a cast iron skillet or baking dish. Add eggplant, zucchini, garbanzo beans, yellow squash, onion, kalamata olives, and garlic to cast iron skillet. Sprinkle 2 teaspoons rosemary over vegetable mixture and toss to coat vegetables in oil.
Bake vegetables in the preheated oven on the bottom rack until slightly tender, about 20 minutes.
Heat the remaining coconut oil in a frying pan over medium-high heat; place sardines in the hot oil and sprinkle with garlic powder and the remaining rosemary. Fry sardines until heated through, about 5 minutes. Top roasted vegetables with sardines and feta cheese.