Prepare halibut as you desire -- I like it either poached or dusted in flour then sautéed. 

In a sauce pan, simmer garlic and shallots in the sherry until liquid is almost gone. 

Add the chicken broth, simmer until liquid is almost gone. 

Add heavy cream, simmer until it starts to thicken. 

Add butter.  Add the avocado, tomatoes and cilantro and heat through.

Serve halibut over rice and top with the avocado-cilantro cream sauce.