Make the sauce: In a small saucepan, combine soy sauce, maple syrup, rice vinegar, mirin (if using), ginger, garlic, and sesame oil. Bring to a gentle simmer over medium heat.
Thicken the glaze: Stir the cornstarch slurry, then whisk it into the saucepan. Simmer 1–2 minutes until glossy and slightly thick.
Remove from heat. Reserve about 1/4 cup for drizzling.
Prep the salmon: Pat salmon dry and season lightly with salt and pepper. This helps sear and keeps flavors balanced.
Cook the salmon: Heat oil in a large nonstick skillet over medium-high.
Place salmon presentation-side down and sear 3–4 minutes until golden. Flip and cook 2–4 more minutes, depending on thickness, until nearly done.
Glaze and finish: Reduce heat to medium-low. Spoon or brush most of the teriyaki sauce over the salmon.
Cook 30–60 seconds, just until the sauce bubbles and coats the fish. Avoid overcooking.
Assemble the bowls: Add warm rice to each bowl. Top with glazed salmon, cucumbers, carrots, avocado, and scallions.
Garnish: Sprinkle with sesame seeds and a squeeze of lime, if you like.
Drizzle the reserved sauce over the bowls.
Serve: Enjoy right away while the salmon is tender and the rice is hot.