Preheat oven to 400 degrees. Cover a large baking sheet with aluminum foil. Line bacon up on sheet pan and bake until crisp, about 10-12 minutes. While the bacon cooks, make the dressing.
For the dressing: Add avocado, yogurt, olive oil, water, lemon juice, garlic, mustard, agave, tarragon, cilantro, salt and pepper to the bottom of a food processor. Turn on and blend until smooth, you may need to stop once or twice to scrape the sides down with a rubber spatula. If you like a thinner consistency, add a little bit more water. Season to taste with salt and pepper. Pour into a dish and set aside.
Once the bacon is done cooking, remove and drain on a paper towel, but reserve grease. Reduce heat on the oven to 350 degrees. Add bread cubes to a large bowl. Use 1 tablespoon of the bacon grease to drizzle on top of the bread along with 1 tablespoons of olive oil. Toss until the grease has evenly coated the bread cubes. Sprinkle with 1/2 teaspoon garlic powder, 1/2 teaspoon dried tarragon and 1/2 teaspoon salt. Toss to evenly coat. Remove foil from baking sheet and spread bread cubes on the clean pan. Bake 12-15 minutes, tossing halfway through until bread is toasted and golden brown.
While the croutons cook, cook the chicken and zucchini. Coat chicken and zucchini with remaining olive oil. Sprinkle both sides of chicken breasts evenly with 1 teaspoon salt, 1 teaspoon garlic powder and a little bit of black pepper. Season zucchini on both sides with salt and pepper. Heat a grill, grill pan or large sauté pan to a medium heat. Once hot, add chicken and zucchini. Cook until brown on both sides and cooked through, about 5-6 minutes per side. (Remember, you should have either small chicken breasts or very thinly sliced chicken breasts, so they cook relatively fast.)
Once chicken and zucchini are done cooking, let them rest for a few minutes. Slice chicken, zucchini and bacon.
To assemble: Toss brussels sprouts, bacon, zucchini, and half of the croutons together with dressing. Season to taste with salt and pepper. Top the salad with sliced chicken, sliced avocado and remaining croutons. Serve immediately.