Step 1

Combine rice and water in a medium saucepan over medium-high heat; bring to a boil. Reduce heat to low, cover, and cook until liquid is absorbed, about 20 minutes (do not uncover while cooking.) Remove pan from heat and let stand, covered, for 10 minutes.

Step 2

While rice stands, combine 2 tablespoons vinegar and sugar in a small microwave-safe bowl; microwave on high until boiling, 30 to 45 seconds. Stir mixture with a whisk until sugar dissolves. Add cream cheese and 1/2 teaspoon salt to bowl, stirring with a whisk to combine. Gently fold vinegar mixture into rice using a rubber spatula; let stand for 5 minutes.

Step 3

Generously coat 12 muffin cups with cooking spray. Lightly coat each of 12 (5-inch square) parchment paper pieces with cooking spray; press paper squares into muffin cups to form a liner. Using moistened hands, press rice mixture evenly along bottom and sides of muffin cups (about 2 1/2 tablespoons rice per cup). Refrigerate for 30 to 40 minutes.

Step 4

Combine remaining 2 teaspoons vinegar, remaining 1/2 teaspoon salt, soy sauce, sesame oil, and red pepper in a medium bowl, stirring with a whisk. Add tuna, cucumber, green onions, and avocado to bowl. Toss gently to combine.

Step 5

Divide tuna mixture evenly among rice cups; sprinkle evenly with sesame seeds. Gently remove cups from pan by lifting parchment paper edges.