Preheat your oven to 350°F / 175°C.
In an extra-large skillet, heat the olive oil over medium heat.
Add the chopped onions and cook for about 5 minutes until softened.
Stir in the minced garlic and cook for another minute until fragrant.
Add the sliced mushrooms and continue to cook, stirring occasionally, for 5-8 minutes until they are browned and any liquid has evaporated.
Meanwhile, in a large saucepan, cook the zucchini and Swiss chard in a small amount of boiling, lightly salted water for 3-5 minutes until just crisp-tender.
Drain the vegetables *thoroughly* in a colander, pressing gently to remove as much excess water as possible.
Stir the drained zucchini and chard into the mushroom mixture in the skillet.
Transfer this entire vegetable mixture to an ungreased 2-quart baking dish and spread evenly.
In a medium bowl, whisk together the lightly beaten eggs, ricotta cheese, milk, Parmesan cheese, fresh dill, salt, and pepper until smooth.
Pour the ricotta mixture evenly over the vegetables in the baking dish.
Bake, uncovered, for 30-35 minutes. The bake is done when the center is set (it should only jiggle slightly) and the top is a beautiful golden brown.
Let it stand for 10 minutes before serving to allow it to set up completely.
Squeeze the Greens: Zucchini and chard hold a lot of water.
After boiling, press them firmly in a colander to squeeze out excess moisture. This is the key to preventing a watery bake.
