Aside from the fact that the engine is computer controlled...
the reason you don't have mixture control is Diesels don't use that.
Gas engines need to breathe a stochiometric mix of air and fuel, i.e. proportioned correctly so there's just enough fuel for the oxygen admitted. Too fuel-lean and it won't burn. Power is controlled by partially blocking the air intake with throttle plates (hence, vacuum). Getting the mix stochiometric under all conditions is a hard job, and that's what the carburetor does. The mixture control helps you fine tune what the carb cannot.
In a diesel, you gulp in a full shot of air (throttle plates: Gone), and compress to a high compression ratio and high heat. This means when fuel is injected, combustion is both certain and spontaneous. So they don't need spark plugs, and can happily run lean (mixture control: Gone). Spontaneous means the engine intake drawing in a fuel-air mixture is out of the question; it would ignite too soon. The engines are direct injection.
Diesel power is controlled solely by how much fuel is injected per cylinder. That is done at the fuel injection pumps. One pump per cylinder that pumps at the appropriate time in the stroke, driven by a cam. Each pump has an adjustment that decides how much fuel is injected. And this is controlled by a "fuel rack" which sets all pumps the same, and the fuel rack is the "throttle".
I always thought diesel's simplicity would make it ideal for aircraft, but the high compression ratio requires stronger cylinders and makes diesel engines heavier, and that's an issue.
Of course nowadays, in their mad pursuit for EPA Tier 4 emissions, they use computers. One common trick is to eliminate the mechanical cam and rack with sensors and EFI to inject at the right time. But they don't have to do that. It's a reliability vs emissions numbers call.