Saute the olive oil, onions, and ginger in a large saute pan over medium-low heat for 10 minutes, or until the onions are translucent. Add the garlic and cook for 1 more minute. Add the mangos, reduce the heat to low and cook for 10 more minutes. Add the orange juice, brown sugar, salt, black pepper, and jalapeno; cook for 10 more minutes, until orange juice is reduced, stirring occasionally. Remove from the heat and add the mint. Serve warm, at room temperature, or chilled.
Heat a saute pan over high heat for 5 minutes until very hot. Season the tuna liberally with salt and pepper. When the pan is very hot, add a drizzle of olive oil and then the tuna steaks. Sear for 2 to 3 minutes on each side, or until the outside is browned, but the inside is very rare.
Serve the tuna on top of the mango salsa.