Make the marinade: in a bowl or large zip-top bag combine 1/2 teaspoon ground ginger, 2 minced garlic cloves, 1 tablespoon soy sauce, 2 tablespoons hoisin sauce, and 2 tablespoons sesame oil. Add the salmon and refrigerate to marinate for 30–60 minutes.
Preheat the oven to 375°F (190°C) while the salmon finishes marinating.
Make the dressing: whisk together 1 minced garlic clove, 1 teaspoon rice vinegar, 1.5 teaspoons lemon juice, a pinch of ground ginger, and salt and pepper to taste in a small bowl.
Toast the sesame seeds: heat a small dry skillet over medium-high heat, add 1 teaspoon sesame seeds, and shake or stir constantly until they turn light brown, about 1–3 minutes. Remove from heat and let cool, then stir into the dressing.
Bake the salmon: place the marinated salmon on a foil-lined baking sheet and bake for 10–15 minutes (depending on thickness) or until cooked through. Remove from oven and let rest briefly.
Prepare the salad: slice the avocado, cucumber, and spring onions. Toss them with the salad greens and the toasted sesame dressing until evenly coated.
Assemble and serve: top the dressed salad with the cooked salmon. Squeeze extra lemon juice and season with additional salt and pepper if desired, then serve immediately.