50 Cent's ex-baby mama, Shaniqua Tompkins, got a restraining order this morning against the rapper - then got served with a huge-ass lawsuit.

Lawyers for 50 Cent took it to Shaniqua Tompkins, slapping her upside the head with a $20 million defamation suit in Connecticut court.

The suit was filed against Tompkins for accusing Fiddy - over and over again - of burning down his own house as well as trying to kill her.

Not only that, 50 wants the court to force Shaniqua to let him visit their 11-year-old son, Marquise, in accordance with an earlier order.

Shaniqua Tompkins also says 50 Cent tried to kill Marquise, naturally.

Both 50 Cent and Shaniqua will appear in a New York courtroom in July to sort it all out, providing neither is assassinated prior to that.

The arson investigation in the fire that torched da crib is ongoing.