In a bowl, whisk together parsley, cilantro, minced garlic, diced jalapeño, lime juice, kosher salt, oregano, and 2 tablespoons olive oil.
Gently fold diced avocado into the herb mixture, taking care not to mash it.
Brush the cleaned portobello mushrooms generously with olive oil to prevent sticking.
Place mushrooms in a shallow dish and pour the avocado herb marinade over them. Cover and let marinate for at least 10 minutes.
Meanwhile, combine balsamic vinegar, soy sauce, garlic powder, black pepper, cayenne, rosemary, and 1 tablespoon olive oil in a small bowl to make the Yummy Goodness Sauce.
Preheat grill to medium heat, about 350-400°F (175-200°C).
Grill portobello mushrooms for about 5 minutes on one side, brushing with Yummy Goodness Sauce as they cook.
Flip mushrooms and grill for another 5 minutes, continuing to brush with the sauce, until tender and nicely charred.
Remove mushrooms from grill and spoon any remaining avocado herb marinade on top before serving.
Serve warm as a main dish or as a flavorful side, enjoying the fresh, zesty, and smoky combination.