Place all dressing ingredients, except salad oil, into a small mixing bowl and whisk together. While whisking add oil in a slow and steady drizzle. Set aside.
In a shallow dish combine the sesame seeds and ground almonds and mix together.
Season tuna with salt and pepper and dredge in sesame mixture until fully coated.
Place a medium skillet over medium-high heat and add half of each oil. Sear tuna for 1 to 2 minutes on each side (for all sides), and transfer onto a cutting board. Set aside.
Add remaining oil to pan and sauté mushrooms for 2 to 3 minutes. Season with salt and pepper.
Transfer mushrooms to a medium mixing bowl and toss together with mixed greens and dressing.
To assemble: Slice tuna into ¼ inch slices. Divide mushrooms and greens mixture between two salad plates, top with sliced tuna and finish with green onions. Serve immediately.