In a large bowl, toss beef with ginger, 2 garlic cloves, pepper and 1/2 teaspoon salt; let stand 15 minutes. In a small bowl, whisk coconut milk, sugar, chili sauce, lime zest, lime juice and remaining salt until blended.

In a large skillet, heat 1 tablespoon oil over medium-high heat. Add beef; stir-fry until no longer pink, 2-3 minutes. Remove from pan.

Stir-fry red pepper, red onion, jalapeno and remaining garlic in remaining oil just until vegetables are crisp-tender, 2-3 minutes. Stir in coconut milk mixture; heat through. Add spinach and beef; cook until spinach is wilted and beef is heated through, stirring occasionally. Sprinkle with green onions and cilantro.