What is the meaning of "Oseh Mishpat la'Ashukim"?
Radak: In every generation He does Mishpat for them against their oppressors. And so He did for Yisrael, who were oppressed in Galus - "Ashukim Bnei Yisrael u'Vnei Yehudah Yachdav v'Chol Shoveihem Hecheziku Vam Me'anu Shalcham" (Yirmeyah 50:33). And so He will do for Yisrael who are oppressed in this Galus.
When does He give food to the hungry?
Radak: In every generation, and so He did for Yisrael in Galus. And when they leave Galus, to go via Midbaros, "Lo Yir'avu v'Lo Yitzma'u v'Lo Yakem Sharav va'Shamesh" (Yeshayah 49:10).
When does "Hashem Matir Asurim" apply?
Brachos 60b: In the morning, when one sits up straight, he should say 'Baruch Matir Asurim.'
Yuma 35b: Eshes Potifar threatened Yosef, if you will not consent to me, I will incarcerate you! He answered, "Hashem Matir Asurim."
Radak: In every generation. And so He did to Yisrael - He released the incarceration of their Galus.
Malbim: If a human king releases a prisoner, he already did enough Tzedakah and Chesed with him; he will not give to him his other needs. However, Hashem releases the bound, and then oversees their needs - to do Mishpat against their oppressors, to punish those who bound them without reason, and also feeds the hungry, lest those who leave prison die of hunger.
Lev Eliyahu (Shemos p.194): It is also for people who bound themselves in the ropes of the wagon of sin.