Cook the quinoa or rice according to package instructions until fluffy; keep warm.
In a small mixing bowl, whisk together the sour cream, Dijon mustard, lemon juice, half of the garlic powder, and the chopped herbs to create the creamy sauce. Cover and refrigerate.
Pat the steak dry with paper towels. Season both sides generously with salt, black pepper, smoked paprika, and the remaining garlic powder.
Toss the zucchini rounds with 1 tablespoon of olive oil, salt, and pepper in a large bowl.
Preheat a grill or heavy grill pan over medium-high heat. Lightly oil the grates.
Grill the steak for 4 to 5 minutes per side for medium-rare (internal temperature of 130°F). Transfer to a cutting board and let rest for 7 minutes.
While the steak rests, grill the zucchini slices for 2 to 3 minutes per side until tender and clearly marked with char lines.
Slice the rested steak thinly against the grain.
Assemble the bowls by layering the grains at the base, followed by a portion of grilled zucchini and steak slices.
Drizzle the prepared creamy sauce over each bowl and garnish with additional fresh herbs if desired.