In a medium bowl, combine cucumber, bell pepper, tomatoes, and onion. Sprinkle with salt and lemon juice. Toss gently, cover, and refrigerate until ready to serve.
Cook the Beef
In a medium pot, combine beef, ginger, lemon juice, turmeric, chili, and salt. Add water, bring to a boil, and cook over medium heat for 30 minutes. Drain, remove the chili, and set the broth aside.
Start the Pilau
In a large pot, heat vegetable oil over medium heat. Add the beef and cumin seeds, stirring until fragrant.
Stir in potatoes and cook until browned on the outside. Add garlic, then carrots, cooking until lightly browned. Add onions and peas, cooking until just tender.
Add the pilau spice blend and coat the beef and vegetables well.
Stir in the rice and beef, then pour in the reserved beef broth. Cover and cook over medium heat for about 30 minutes, until the rice is tender and the liquid is absorbed.
In Kenya and Tanzania, pilau is often slow-cooked over coal stoves. Coals are placed under the pot and on the lid to evenly cook the rice for up to 1 hour.
Fluff the pilau with a fork and serve hot with chilled kachumbari on the side.