Combine ingredients in a medium saucepan and bring to a boil. Let sit overnight. Strain and set aside. Slice cucumber into thin strips lengthwise. Saute garlic and shallots over medium heat for two minutes. Add honey and soy sauce. Remove from heat and stir in Chinese mustard, cucumber and tomato. Let sit for at least 2 hours.
Place tuna and salmon slices lengthwise on a cutting board and cover with plastic wrap. Gently pound slices with a knife handle or meat tenderizer.
Cut the salmon and tuna slices into 1 1/2-inch strips. Lay two of the salmon slices next to each other. Place two slices of tuna on top of salmon. Roll the salmon and tuna strips lengthwise. Form a rosettes by gently pushing the top of the roll outward.
To serve: Spoon a small amount of cucumber salad onto each plate. Place tuna salmon rosettes on the salad.
Bring citrus oil to a boil.
Pour 1/2 tablespoon of hot citrus oil over the rosette and serve immediately.