How to Make It
In a small saucepan, combine the pineapple juice and honey and bring to a boil. Simmer over moderately low heat until reduced to 1/2 cup, about 25 minutes. Let cool.
Roast the red and yellow peppers directly over a gas flame or under the broiler, turning, until charred all over. Transfer to a bowl, cover and let steam for 10 minutes. Peel the peppers and discard the stems and seeds.
Cut the peppers into 1/2-inch dice and put them in a large skillet. Add the reserved pepper juices and the red and yellow tomatoes and boil over moderately high heat for 2 minutes. Add the sun-dried tomatoes, season with salt and pepper and remove from the heat.
Light a grill or preheat a grill pan. Season the tuna steaks with salt and pepper. Grill the tuna steaks over a hot fire or over high heat for 2 to 3 minutes per side, brushing frequently with the pineapple and honey glaze; the tuna should be nicely charred on the outside and medium rare within.
Bring the pepper ragout to a simmer. Remove from the heat and swirl in the butter until blended. Set a tuna steak on each plate and spoon the pepper ragout alongside. Garnish with the oregano and serve at once.