Make sure tuna is very fresh (you can substitute another fish if you like such as wild salmon or scallop if you have expensive tastes), clean off all the connective tissue, dice small or larger if you prefer. Keep refrigerated.
Add all the ingredients together and season to taste, refrigerate
In a separate bowl, toss the sprouts & radish with a squeeze of lemon juice & olive oil to coat. Season with salt & pepper.
Place a serving of tuna tartare on a plate, top with pinch of salad and drizzle again with olive oil. Serve with a crostini or a vessel of your choosing