Preheat oven to 400 degrees F.
Marinate cucumbers. Whisk together rice vinegar, soy sauce, sugar, and sesame oil until sugar is dissolved. Pour over sliced cucumber and jalapeno, stirring to combine. Let sit for at least 30 minutes.
Mix mayonnaise with tobiko and gochujang until well combined. Season aioli with salt and pepper and let aside.
Make unagi sauce. Combine mirin, soy sauce, sugar, and sake in a small sauce pot. Bring to a boil over high heat, then reduce heat to low and continue to simmer for 5 minutes or until slightly thickened. Remove from heat.
Cut salmon into bite-size chunks. Season with salt and pepper and lay in an even layer on baking sheet. Bake for 8-10 minutes or until flesh flakes easily. Drizzle unagi sauce on top, reserving remaining sauce for serving.
Heat 2 tablespoons oil and 1 tablespoon oil in a large saute pan. Add sesame seeds and cook for 1 minute. Add rice and press into an even layer. Let sit undisturbed for 5 minutes or until golden brown on the bottom. Stir rice.
Portion rice into 4 bowls and top with salmon, marinated cucumbers and jalapeno, tobiko gochujang aioli, and avocado. Drizzle extra unagi sauce on top and sprinkle furikake. Serve immediately.