Heat oven to 400 degrees F, Line a baking sheet with parchment paper.
Heat grill to medium / high heat
Slice the portobello mushrooms into strips. Place them in a bowl and drizzle them with olive oil, soy sauce, balsamic, garlic and freshly ground black pepper. Use your hands to coat the mushrooms on all sides.
Place mushrooms on baking sheet and bake mushrooms for 12-15 mins until they are nice and tender
While the mushrooms are cooking, its time to make the chimichurri sauce
To make the chimichurri: Combine shallot, chillies or jalepenos, garlic, vinegar, and 1 tsp. salt in a medium bowl. Let sit 10 minutes. Stir in cilantro, parsley, and oregano. Using a fork, whisk in oil.
While the mushrooms are cooking, place corn on the grill and cook for 12-15 minutes
Remove the corn from the grill and let cool a few minutes
Once the corn has cooled, cut the fresh corn off the cob and set aside
Assembly
To assemble the tacos, place 4-5 slices of mushroom in the center of the tortilla, followed by 1-2 slices of avocado, sliced red onions, a spoonful of chimichurri, then sprinkle with crumbled feta and hot sauce (optional)
Serve immediately