Combine vegetable oil, sesame oil, soy sauce, brown sugar, minced garlic, grated ginger, and black pepper in a bowl and whisk until the sugar dissolves.
Add flank steak and coat thoroughly; marinate for at least 30 minutes or up to overnight.
Cook jasmine rice until fluffy and separate.
Chop green onions, shred carrots, and slice cucumber into thin matchsticks.
Whisk mayonnaise, sriracha, lime juice, honey, and a pinch of salt until smooth and adjust heat to taste.
Heat a heavy skillet over high heat until very hot, add a tablespoon of neutral oil to coat.
Sear the marinated steak 3-5 minutes per side until a dark crust forms and interior reaches about 125-130°F for medium-rare.
Rest steak on a cutting board for 5-10 minutes, then slice thinly across the grain.
Divide warm jasmine rice among bowls, top with sliced steak, green onions, shredded carrots, cucumber, and drizzle with spicy cream sauce.
Finish with an extra squeeze of lime or a dash of sriracha to taste.