In a medium bowl whisk the oil, oregano, chili powder, cumin, salt, and pepper. Add the shrimp and toss to coat.
In another medium bowl whisk the oil, oregano, salt, and pepper. Add the zucchini and toss to coat.
Prepare the grill for direct cooking over medium heat (350° to 450°F) and high heat (450° to 550°F).
Place the apricot halves on a plate and brush with the oil. In a small bowl whisk the honey, lime juice, and serrano chile. Set aside.
Brush the cooking grates clean. Grill the apricot halves over direct medium heat, with the lid closed, until slightly softened and grill marks appear, 6 to 9 minutes (depending on ripeness of the fruit), turning once or twice. Transfer the apricots to a cutting board. Let cool slightly, then dice. Add the apricots to the honey and lime juice mixture and stir in the cilantro. Toss to combine. Season with the salt and pepper. Taste and add more honey ½ teaspoon at a time, if desired.
Place a perforated vegetable basket over direct medium heat and preheat for about 5 minutes. Spread the zucchini in a single layer on the vegetable basket and cook, with the lid closed, until just tender, 4 to 6 minutes, turning once or twice. At the same time, grill the shrimp over direct high heat, with the lid closed, until they are firm to the touch and just turning opaque in the center, 4 to 6 minutes, turning once or twice. Remove the shrimp and the vegetable basket with the zucchini from the grill. Grill the tortillas over direct medium heat until slightly charred on both sides but still soft, 1 to 2 minutes, turning once.
Place one tortilla on each of four plates and divide the zucchini slices among the tortillas. Top the zucchini with the shrimp, and then the salsa, dividing them evenly. Sprinkle the feta over each tostada and serve immediately.